MaraMedia
TECHNOLOGY
LEARNER MANUAL
GRADE 9
Memorandum Book
1
MODULE 1: STRUCTURES
TECH DRAWING
a sharp HB pencil
a ruler
not go over the same line
lines join at the corners
no gaps
when the lines are too long erase the excess
When printing headings, write the letters the same size, clear and neat
do not press too hard when drawing
Show hidden detail with a broken line
Revision of Grade 8
Sketches copied:
Scale
Neatness
Quick Review:
Redraw the following diagram on the isometric grid provided below it:
Redrawn to scale
Isometric drawing
Neatness
Hidden detail
2
1.1.1.
First angle orthographic projection
Orthographic Projection is a way of drawing a 3D object from
different directions. Usually a front, side and plan view are
drawn so that a person looking at the drawing can see all the
important sides.
There are two ways of drawing in orthographic - First Angle and Third Angle. They
differ only in the position of the plan, front and side views.
Whenever you are given a three-dimensional shape and asked to do a first angle
orthographic projection, it helps to colour the shape’s different planes in contrasting
colours – that we, as we have done here, it is easy to see which panels belong to
which view.
Putting these together:
Front View
Side View
45˚
Top View
Orthographic projection (or orthogonal projection) is a means of representing a
three-dimensional object in two dimensions.
The web-site: http://metal.brightcookie.com/2_draw/draw_t3/htm/draw3_2_4.htm
demonstrates beautifully how this is done:
3
The word “Ortho” is a Greek word that means right or true. In this system of
projection, the 3D object is projected perpendicularly onto a projection plane with
parallel projectors. You can project in six orthogonal directions. The resulting views
are called basic views. You may imagine that the 3D object is placed inside a
transparent box, and views are projected orthogonally onto the six walls of the box:
Because it is inconvenient to carry the box around, the box is cut open and spread
out onto a common plane. This plane is the plane of the drawing paper:
4
ACTIVITY: First angle orthographic projections of the shapes shown below:
You need to rotate your drawing pages to landscape.
1.
SKETCH 1:
2.
SKETCH 2: (Use a scale of 1:3):
5
3.
SKETCH 3: (Use a scale of 1:2):
4.
SKETCH 4:
6
5.
SKETCH 5:
6.
SKETCH 6:
7
7:
SKETCH 7:
8.
SKETCH 8:
8
The same thing, but in reverse – make an isometric (3-D) drawing of the given first
angle orthographic projection
9
1.1.2.
Line types & Scale and dimension
Line types: Dark; Feint; Dashed; Wavy; Chain
Different types and thicknesses of lines on a drawing represents specific precice information
regarding the design.
Function
Visible outlines
Dimension lines
Hidden detail
Broken
Centre lines
Developed views
0,7
0,3
0,3
0,3
0,3
0,3
Thickness / Type
mm Continuous
mm Continuous
mm Dashes - short
mm Continuous wavy
mm Long chain
mm Short chain
Example
Study the following technical drawing provided and identify the four line types and thicknesses used:
1
2
3
4
Line type
Visible outlines
Hidden detail
Centre lines
Dimension lines
0,7
0,3
0,3
0,3
mm
mm
mm
mm
Thickness
Continuous
Dashes - short
Long chain
Continuous
Exploded view.
An exploded view enables us to see how different part are put together to make up an object. The
view below shows how the object has been manufactured and then how to assemble it.
Hidden detail.
In order to show hidden detail we use broken lines these lines and the gaps are of equal length
normally 2mm or 3mm long. These broken lines allows us to see inside the box.
Scale and dimensions:
Drawing to scale is a tool that Engineers use for many different tasks. You have been taught how to
work with scale in drawings in Mathematics as well as in Geography. One key part of every scale
drawing is the scaling factor. This number represents the degree to which your scale drawing or scale
model has been reduced in size when compared to the original. Scaled drawings are a means of
communication between the contractor and the designer of a structure. Scaled drawings are used
because they allow the designer to put a large amount on information into a relatively small and
easily read package.
10
ACTIVITY: Design Problem
The design will be assessed according to the following rubric:
5
Criteria
Superb
4
Good
3
OK
2
Needs
attention
1
Disappointing
Initial ideas
Free-hand sketches
Design brief with specifications and
constraints
Use of scale and conversions
Isometric projection
First angle orthographic drawing
Total / 30
1.2.
Forces
ASSIGNMENT: Examples of forces
Give two examples of each type of force listed in the table below. Try and get
examples from your everyday life.
Static Forces
Dynamic Forces
Compressive Forces
Torsional Forces
a simple electric, magnetic or gravitational fields
carrying a weight of books but walking
"skating" in your socks on your kitchen floor
A spring would stretched and would give it less force
to pull
impacted fractures or compression fractures
twisting the lid off a container
plastic ruler is twisted between both hands
the forces found in the human body depicted in the table below:
Dynamic
torsional
compressive
11
ACTIVITY: Types of forces
N
K
N
O
I
S
S
E
R
P
M
O
C
D
Z
O
J
C
W
W
F
F
O
O
D
K
V
T
H
L
Type of force
friction
torsional
gravitation
compression
centrifugal
tensile
static
dynamic
electrical
cohesive
adhesive
I
I
J
I
J
R
G
B
Y
D
W
V
N
C
H
T
B
T
N
T
E
L
R
F
U
P
C
O
C
A
A
U
E
Q
T
A
S
A
C
N
V
K
I
A
D
T
D
N
T
O
L
T
U
Z
M
S
E
T
J
H
I
Q
S
G
R
Q
T
S
T
W
E
M
C
C
E
V
B
I
C
S
E
F
Y
O
W
X
Y
I
Z
S
A
D
L
M
I
T
L
M
W
R
E
Y
R
R
I
R
Y
E
F
O
M
L
J
V
B
T
P
F
O
V
G
N
U
K
N
K
B
X
O
E
Z
C
U
J
E
Z
A
R
L
A
G
U
F
I
R
T
N
E
C
I
Y
M
S
U
L
T
D
I
Q
J
G
J
O
L
V
W
I
X
S
E
V
I
S
E
H
O
C
Y
O
E
G
C
U
A
T
X
C
I
T
A
T
S
X
H
B
Definition
the force exerted by a surface as an object moves across it or makes an
effort to move across it.
the force that causes an object to be twisted in one direction and the other
end is held motionless or twisted in the opposite direction.
the force that pulls objects downwards towards the centre of the earth.
the force exerted on an object that causes it to become squashed or
compacted.
the tendency of an object following a curved path to
fly away from the centre of curvature.
the force that is transmitted through a string, rope, cable or wire when it is
pulled tight by forces acting from opposite ends.
the branch of mechanics concerned with the analysis of forces on physical
systems in static equilibrium, i.e. where the relative positions of subsystems
do not vary or are at a constant velocity.
forces that produce a change in motion, as opposed to being static
the forces between particles that are caused by their electric charges.
the intermolecular forces (as in hydrogen bonding and Van der Waals
forces) which cause a tendency in liquids to resist separation.
the attractive forces between unlike molecules. They are caused by forces
acting between two substances, such as mechanical forces (sticking
together) and electrostatic forces.
12
MINI PAT
Working drawings with dimensions. These drawings should include both isometric and first angle
orthographic drawings.
A budget must be submitted as well as a time line of events.
Your group will consist of a CEO (Chief Executive Officer) who is the leader, an engineer, a
draughtsman and an accountant.
You may assist one another!
A working model as per drawing must be submitted.
Criteria
Costs
Drawing
Budget
Model
Safety
9-10
7-8
3-6
0-2
Outstanding, well
Researched,
detailed
Complete.
Material, Labour,
Transport costs
included and
accurate.
Researched but
incomplete/
inaccurate.
Material, Labour,
Transport cost not
detailed enough.
Certain items
researched.
Material,
Labour,
Transport cost
inaccurate
No research or
poor attempt.
Left out Material /
Transport /
Labour cost.
Outstanding; Neat;
Detailed; Scaled:
Complete;
Neat, but
incomplete/
inaccurate
Not neat or
inaccurate /
incomplete.
Incorrect scale.
Unneat, sloppy or
not handed in
Outstanding,well
Researched,
Detailed,
Complete
Researched but
incomplete/
inaccurate
Only certain
items
researched
No research or
attempt
Outstanding; Neat;
Detailed; Scaled:
Complete;
Neat but
incomplete/
inaccurate
Not neat or
inaccurate /
incomplete
Unneat, sloppy or
not handed in.
Haphazzard
attempt.
All aspects covered;
Well thought out.
Railings and other
safety measures
adequate.
Most aspects
covered. Safety
features are in
place but not
sufficient.
Solutions
regarding safety
impractical or
incomplete.
Safety solutions
absent or of very
poor nature
Total / 50
13
The different role players must be assessed as follows:
Leadership of the CEO
Criteria
Maximum Possible Mark
Organsation of tasks
5
Effective and fair delegation
5
Time management
5
Cooperation achieved
5
Team Accountant
Accurate calculation of
material required
Accurate calculation of labour
cost
Accurate calculation of
transport cost
Obtained proper quotes
5
5
5
5
Draughtsman
Portfolio record of everyone’s
designs
Clear representation of
bridge in 2 D
Clear representation of
bridge in 3 D
Safety aspects considered
5
5
5
5
Engineer
Structure sound
Neat construction
Meets all criteria
Accurate to scale
5
5
5
5
TOTAL
80
14
Actual Mark
MODULE 2:
MECHANICAL SYSTEMS AND CONTROL
2.1.
Syringe mechanics
ACTIVITY:
Investigating simple hydraulic systems:
Syringes of the same size:
What happens to the output plunger when an input force is applied?
Pushes out in same quantity as input plunger is pushed in
Does it move the same or different to the force movement of the force?
Same quantity, opposite direction
How would you get the system back to where you started?
Push output plunger back in.
A small and large syringe.
Apply an input force on the smaller syringe (A) and observe the movement on the larger output
plunger (B).
What happens to the output plunger when an input force is applied?
Pushes out
Does it move the same or different to the input movement of the force?
Pushes out by bigger measure than input syringe was pushed in
Notes:
If the areas of the input and output cylinders are the same the forces will be the same.
If the area of the input piston (the plunger in the syringe) is smaller than the output cylinder then the
output force will be larger.
Small area / small force in the driver cylinder causes a large force in the output cylinder.
If the area of the input piston is larger than the output cylinder then the output force will be smaller.
Large area / large force in driver cylinder causes a small force in the output cylinder.
15
Explain concept of hydraulic lift:
The hydraulic jack works on the same principle. A small cylinder needs only a small amount of force
and movement to produce a large amount of movement and force in a larger cylinder.
This allows a small person to lift a very large truck, or load using a small effort.
Any basic system consists of two cylinders connected by tubing. They can be pneumatic (driven by
air) or hydraulic (driven by water). Hydraulic provides more power (due to the fact that the volume
in the driving cylinder cannot be compressed as much as with air), and more precise control over the
travel of the driven piston.
Explain Hydraulics vs pneumatic system:
If we would repeat the same experiment using air in the syringes (pneumatic system), instead of
water (hydraulic system), we would find that Gases (like air) are compressible while Liquids (like
water and oils) are incompressible.
Explain PASCAL’S PRINCIPLE:
Pascal's law states that when there is an increase in pressure at any point in a confined fluid, there is
an equal increase at every other point in the container.
Pressure exerted on one part of a hydraulic system will be transferred equally without any loss in all
directions to other parts of the system.
Explain how Hydraulic Jack works:
Hydraulic jacks and many other technological advancements such as automobile brakes and dental
chairs work on the basis of Pascal's Principle, named for Blaise Pascal, who lived in the seventeenth
century. Basically, the principle states that the pressure in a closed container is the same at all points.
Pressure is described mathematically by Force divided by Area. Therefore if you have two cylinders
connected together, a small one and a large one, and apply a small Force to the small cylinder, this
would result in a given pressure. By Pascal's Principle, this pressure would be the same in the larger
cylinder, but since the larger cylinder has more area, the force emitted by the second cylinder would
be greater.
This is represented by rearranging the pressure formula P = F/A, to F = PA. The pressure stayed the
same in the second cylinder, but Area was increased, resulting in a larger Force. The greater the
differences in the areas of the cylinders, the greater the potential force output of the big cylinder. A
hydraulic jack is simply two cylinders connected as described above.
A hydraulic lift for automobiles is an example of a force multiplied by hydraulic press, based on
Pascal's principle. The fluid in the small cylinder must be moved much further than the distance the
car is lifted.
16
Activity:
Using the same lift information as in the example, i.e. a 25 cm diameter lift cylinder and 1,25 cm
diameter driver cylinder, calculate the force required to lift:
1. a car of mass 750 kg. Remember that you will need to convert the mass to a weight first by
multiplying it by ten (W = mg). We use ten as our gravitational constant for the purpose of this
exercise, even though that is a grossly rounded off figure (g = 9,8 m.s-2)
Weight= 7 500 N
𝐹1 =
𝐹1 =
𝐹2 𝐴1
𝐴2
7500 × 1,25
25
𝐹1 = 375𝑁
2. a truck of mass 2500kg:
Weight=2 5000 N
𝐹1 =
𝐹1 =
𝐹2 𝐴1
𝐴2
25000 × 1,25
25
𝐹1 = 1750𝑁
3. a luggage trailer of 85 kg:
Weight= 850 N
𝐹1 =
𝐹1 =
𝐹2 𝐴1
𝐴2
850 × 1,25
25
𝐹1 = 42,5𝑁
17
Force
In physics, a force is any influence that causes an object to undergo a change in speed, a change in
direction, or a change in shape. In other words, a force is that which can cause an object with mass
to change its velocity (which includes to begin moving from a state of rest), i.e., to accelerate, or
which can cause a flexible object to deform. Force can also be described by intuitive concepts such as
a push or pull.
By pushing or pulling on an object we give it energy and cause it to move, stop moving, or change
direction. For example, when we lift a glass of water, we exert force on it to cause it to lift in the air.
Similarly, the water in the glass exerts a force on the wall of the glass.
The force may produce motion of the body or may cause the body to deform.
Energy may be expended in the process, or the applied force may be balanced by an
opposing force so that no energy is expended.
Pulleys
Pulley systems are used in the real world to lift large masses onto tall heights. You might have seen
the workers repairing the roof of a house and using the pulley system to lift their tools or materials to
the roof. A pulley is an example of a simple machine.
The pulley system consists of one or more pulleys and a rope or a cable. The number of pulleys used
may increase or decrease the mechanical advantage of the system. Generally, the higher the
mechanical advantage is, the easier it is to lift the object that is being lifted.
The load that has to be lifted is indicated by the Tension (T) in each of the combined
movable pulley systems illustrated below:
18
By adding more pulleys to the system, the Tension (Load) that can be lifted is increased as the total
load gets divided amongst the different cables connecting the pulleys. The load is shared equally
amongst the cables, making lift easier.
Explain how Pulleys are used on elevators:
The most popular elevator design is the roped elevator. In roped elevators, the car is raised and
lowered by traction steel ropes rather than pushed from below.
The ropes are attached to the elevator car, and looped around a sheave. A sheave is just a pulley
with grooves around the circumference. The sheave grips the hoist ropes, so when you rotate the
sheave, the ropes move too.
The sheave is connected to an electric motor. When the motor turns one way, the sheave raises the
elevator; when the motor turns the other way, the sheave lowers the elevator. In gearless elevators,
the motor rotates the sheaves directly. In geared elevators, the motor turns a gear train that rotates
the sheave. Typically, the sheave, the motor and the control system are all housed in a machine room
above the elevator shaft.
The ropes that lift the car are also connected to a counterweight, which hangs on the other side of
the sheave. The counterweight weighs about the same as the car filled to 40-percent capacity. In
other words, when the car is 40 per cent full (an average amount), the counterweight and the car are
perfectly balanced.
The purpose of this balance is to conserve energy. With equal loads on each side of the sheave, it
only takes a little bit of force to tip the balance one way or the other. Basically, the motor only has to
overcome friction -- the weight on the other side does most of the work. To put it another way, the
balance maintains a near constant potential energy level in the system as a whole. Using up the
potential energy in the elevator car (letting it descend to the ground) builds up the potential energy in
the weight (the weight rises to the top of the shaft).
We also need to distinguish between fixed and movable pulley systems. (p.52)
Number of pulleys
Fixed Pulley System
Single wheel
Double wheel
19
Movable Pulley System
ACTIVITY: (p.53) The Load on Pulley Systems:
1.
Suppose you could lift 340 N. with a two-wheeled pulley.
How much weight could you lift with the following pulleys?
2.
Sketch
Weight
𝑊 = 340 × 4
𝑤 = 1360𝑁
Mass
𝑊
𝑚=
10
1360
𝑚=
10
𝑚 = 136𝑘𝑔
Sketch
Weight
𝑊 = 340 × 3
𝑤 = 1020𝑁
Mass
𝑊
𝑚=
10
1020
𝑚=
10
𝑚 = 102𝑘𝑔
Sketch
Weight
𝑊 = 340 × 6
𝑤 = 2040𝑁
Mass
𝑊
𝑚=
10
2040
𝑚=
10
𝑚 = 204𝑘𝑔
Sketch
Weight
𝑊 = 340 × 5
𝑤 = 1700𝑁
Mass
𝑊
𝑚=
10
1700
𝑚=
10
𝑚 = 170𝑘𝑔
Repeat the exercise for the following two pulley set-ups for lifting 28 kg:
Sketch
Weight
𝑊 = 280 × 4
𝑤 = 1120𝑁
Mass
𝑊
𝑚=
10
1120
𝑚=
10
𝑚 = 112𝑘𝑔
Sketch
Weight
𝑊 = 280 × 5
𝑤 = 1400𝑁
Mass
𝑊
𝑚=
10
1400
𝑚=
10
𝑚 = 140𝑘𝑔
3. Engineers use pulleys in all sorts of applications. Your challenge is to design a plan that uses two
pulleys to life up a soda bottle. Draw your plan in the box below:
20
Do you expect the force you will have to apply to move the bottle will be reduced? By how much?
Yes – will be reduced to half of original force.
4. Draw a plan for using four pulleys to lift your soda bottle:
Do you expect the force you will have to apply to move the bottle will be reduced? By how
much?
5.
Yes – reduced to a quarter of original force
Can you think of examples of two machines that incorporate pulley systems?
1
2
6.
Exercise machines ; Drill press; Timing belt in car…..
Block-and-tackle; Escalators; elevators……..
Can you think of engineering problems that were solved through the use of a pulley or a
pulley system?
Lifting heavy building material
Pulling engines from cars
Lifting pipes from boreholes
7.
Do you think the smoothness of the rope or twine pulley impacts how much force is needed
to lift an object?
YES
NO
Motivate your answer: Less friction
8.
when rope is smoother
Do you think the size of the pulley impacts how much force is needed to lift
an object?
YES
NO
Motivate your answer:
The bigger the pulley, the less rotation for force applied
21
Ratchet and pawl:
A winch or a crane needs to be able to hold a load without it
slipping or moving. The ratchet consists of a spur gear with
the teeth cut slanted to one side and the pawl fits into these
gear teeth and stops the gear from rotating in the opposite
direction.
Ratchets and pawls are mechanical assemblies that are used
to transmit intermittent rotary motion, or to permit a shaft to
rotate in one direction but not the other.
Ratchets and pawls are usually made of steel, stainless steel,
cast iron, brass, or other metal materials.
Ratchets are sometimes called ratchet wheels because they consist of a rotating gear or rack with
angled teeth. Pawls, which are sometimes misidentified as ratchets, are thin protrusions that rest
against a ratchet to restrict its motion.
When the ratchet is rotated in one direction, the pawl is raised and moves
smoothly between the angled teeth.
When the ratchet’s rotation stops, the pawl rests between the teeth and
makes a clicking noise.
Ratchets and pawl that permit rotation in only one direction cause the pawl
and teeth to clash if the ratchet is turned the opposite way.
Applications for these single-direction devices include turnstiles
and winders.
Name three other applications of this mechanism:
1
2
3
Ratchet socket wrench or spanner
Clocks
Wind-up toys
The action of a ratchet can be either harsh or smooth, depending on the
configuration of the ratchet teeth and pawl.
22
Explain concept: DISC BRAKE
The disc brake or disk brake is a device for slowing or stopping the rotation of a wheel while it is in
motion.
A brake disc is usually made of cast iron, but may in some cases be made of composites such as
reinforced carbon–carbon or ceramic matrix composites. This is connected to the wheel and/or the
axle. To stop the wheel, friction material in the form of brake pads (mounted on a device called a
brake calliper) is forced mechanically, hydraulically, pneumatically or electromagnetically against both
sides of the disc. Friction causes the disc and attached wheel to slow or stop. Brakes convert motion
to heat, and if the brakes get too hot, they become less effective, a phenomenon known as brake
fade.
Explain how a BICYCLE BRAKE works:
Inadequate braking is often the result of a loose brake cable on one or both bike wheels. Place a third
hand -- a special tool available at bike shops -- over the brake shoes; use it to draw the brake shoes
into contact with the wheel rim.
With an adjustable wrench, loosen the cable clamp nut that secures side-pull brakes or the cable
anchor bolt that secures center-pull brakes. Grip the end of the cable with pliers and pull the cable
through the clamp or anchor until it's tight; holding the cable tight with one hand, tighten the cable
clamp nut or cable anchor. Release the brake.
Test the brake by squeezing the brake lever; the brake should grip when the lever is depressed about
1,5 cm. If it doesn't, the cable could still be too loose; repeat the tightening procedure.
Lift the bike so that its front wheel is off the ground, and spin the wheel. If the wheel binds, loosen
the cable a bit. Check the brake levers on the handlebars. If they're stiff or squeaky, spray them with
bicycle spray lubricant at the pivot points.
Explain what a CLEAT is:
A cleat is a piece of wood, metal, or plastic, often wedge-shaped, fastened to something to
strengthen it or give secure footing:
Cleats are used on gangways, under shelves, on the soles or heels of shoes, etc.
In nautical terms, a cleat is a small metal or wood fitting fixed as to the deck of a ship and used to
secure a rope, specifically one with projecting ends:
23
Gears
Gears are machine elements that transmit motion by means of successively
engaging teeth. The gear teeth act like small levers.
SPUR GEARS:
Many machines use spur gears. A very good example is a bicycle that has spur gears
that make it easier to cycle, especially up hills.
Gears have many uses in our lives. They are used to :
multiply or reduce speed and force;
change the direction of motion;
transmit a force over a distance.
Complete the following table: (p.60)
Picture
INVESTIGATION:
Colour
Size
Number of teeth
Red
Small
20
Blue
Medium
40
Yellow
Large
80
Gear Ratio’s – Size, Speed, Rotation
When two gears interact, the first is known as the DRIVER and the second as the
DRIVEN:
DRIVER
DRIVEN
24
What would happen to the direction of rotation if the blue gear is replaced with the yellow gear?
The blue gear rotates clock-wise if the yellow gear rotates anti-clock-wise
The blue gear rotates anti clock-wise if the yellow gear rotates clock-wise
Complete the table below by filling in the direction of rotation of the gears.
Driver
Driven
Driver Direction
Driven Direction
Red
Red
Blue
Blue
Yellow
Yellow
Blue
Yellow
Yellow
Red
Red
Blue
clockwise
Anti-clockwise
clockwise
Anti-clockwise
clockwise
Anti-clockwise
Anti-clockwise
clockwise
Anti-clockwise
clockwise
Anti-clockwise
clockwise
We now place the blue gear (driver) so that it meshes with
the red gear (idler) and with a blue gear as shown in the
picture. An idler is used to synchronise rotation.
Underline the correct option of the terms inside the
brackets:
1.
If the blue gear (driver) rotates clock-wise:


the red gear rotates (clock-wise / anti clock-wise) and
the driven blue gear with rotate (clock-wise / anti clock-wise).
2.
If the blue gear (driver) rotates anti clock-wise:
 the red gear rotates (clock-wise / anti clock-wise) and
 the driven blue gear with rotate (clock-wise / anti clock-wise).
3.
The RED gear is called the IDLER gear. What does it do?
It synchronises rotation
Intermeshing gears are used to transmit motion and force. A series of intermeshing
gears is called a gear train. Intermeshing gears turn in opposing directions.
An understanding of some of the terminology is needed. In a gear train we have a
gear known as the driver and one known as the driven.
Driver - is the gear that has the force or motion input.
Driven- is the gear that results in the force or motion output.
25
Gears spin in opposite directions.
If we were to turn the large gear (driver) we can multiply the number of
turns generated by the smaller gear (driven).
DRIVER
The number of teeth in these gears are 30 and 15, respectively.
DRIVEN
The gear ratio of a gear train is the number of teeth on the driven divided
by the number of teeth on the driver:
𝐺𝑒𝑎𝑟 𝑅𝑎𝑡𝑖𝑜 =
𝑁𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑡𝑒𝑒𝑡ℎ 𝑜𝑛 𝐷𝑟𝑖𝑣𝑒𝑛 𝑔𝑒𝑎𝑟
𝑁𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑡𝑒𝑒𝑡ℎ 𝑜𝑛 𝐷𝑟𝑖𝑣𝑒𝑟 𝑔𝑒𝑎𝑟
In the gear train above the driver has 30 teeth while the follower has 15 teeth.
𝐺𝑒𝑎𝑟 𝑅𝑎𝑡𝑖𝑜 =
=
15
30
𝑁𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑡𝑒𝑒𝑡ℎ 𝑜𝑛 𝐷𝑟𝑖𝑣𝑒𝑛 𝑔𝑒𝑎𝑟
𝑁𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑡𝑒𝑒𝑡ℎ 𝑜𝑛 𝐷𝑟𝑖𝑣𝑒𝑟 𝑔𝑒𝑎𝑟
=
1
2
Therefore the gear ratio is 1/2 . For every turn of the driver the driven gear turns twice.
This gear train can be used to multiply speed on a bicycle if the driven gear was connected to a
wheel and the driver gear connected to the pedals.
DRIVEN
If we were to turn the small gear (driver) we can reduce the number of turns
generated by the larger gear (driven).
The number of teeth in these gears is 15 and 30, respectively.
DRIVER
To calculate this gear ratio:
In the gear train above the driver has 15 teeth while the follower has 30 teeth.
𝐺𝑒𝑎𝑟 𝑅𝑎𝑡𝑖𝑜 =
=
30
15
𝑁𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑡𝑒𝑒𝑡ℎ 𝑜𝑛 𝐷𝑟𝑖𝑣𝑒𝑛 𝑔𝑒𝑎𝑟
𝑁𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑡𝑒𝑒𝑡ℎ 𝑜𝑛 𝐷𝑟𝑖𝑣𝑒𝑟 𝑔𝑒𝑎𝑟
=2
Therefore the gear ratio is 2/1 . For every two turns of the driver the driven gear turns only once.
General rule:
Low gear ratio
High gear ratio
= more speed
= less speed
= less force
= more force.
26
Activity (p.63)
GEAR TRAIN 1:
Place the red gear (driver) so it meshes with the blue gear (driven). Make a mark on the red gear and
mark off a spot on the corresponding blue gear:
What do you notice?
For every two turns of the driver (red gear) the driven (blue) gear turns only once.
GEAR TRAIN 2:
We now place the blue gear (driver) so that it meshes with the yellow gear (driven) as shown in the
picture.
What happens when the blue driver is rotated one full revolution?
The yellow driven gear is rotated only a half rotation
Will the driven gear be slower or faster than the driver gear?
slower
GEAR TRAIN 3:
If the yellow gear is the driver and the blue gear is driven, what happens when the yellow driver is
rotated one full revolution?
The blue driven gears goes through two full rotations
Will the driven gear be slower or faster than the driver gear?
faster
GEAR TRAIN 4:
If the red gear is the driver and the yellow gear is driven, what happens when the red driver is
rotated one full revolution?
The yellow gear passes through only a quarter rotation
Will the driven gear be slower or faster than the driver gear?
slower
27
Calculate the Gear Ratio in the gear trains provided on the previous pages:
GEAR TRAIN1:
𝑁𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑡𝑒𝑒𝑡ℎ 𝑜𝑛 𝐷𝑟𝑖𝑣𝑒𝑛 𝑔𝑒𝑎𝑟
𝐺𝑒𝑎𝑟 𝑅𝑎𝑡𝑖𝑜 =
𝑁𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑡𝑒𝑒𝑡ℎ 𝑜𝑛 𝐷𝑟𝑖𝑣𝑒𝑟 𝑔𝑒𝑎𝑟
=
40
20
=2
GEAR TRAIN 2:
𝐺𝑒𝑎𝑟 𝑅𝑎𝑡𝑖𝑜 =
=
80
40
𝑁𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑡𝑒𝑒𝑡ℎ 𝑜𝑛 𝐷𝑟𝑖𝑣𝑒𝑛 𝑔𝑒𝑎𝑟
𝑁𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑡𝑒𝑒𝑡ℎ 𝑜𝑛 𝐷𝑟𝑖𝑣𝑒𝑟 𝑔𝑒𝑎𝑟
=2
GEAR TRAIN 3:
𝐺𝑒𝑎𝑟 𝑅𝑎𝑡𝑖𝑜 =
=
40
80
𝑁𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑡𝑒𝑒𝑡ℎ 𝑜𝑛 𝐷𝑟𝑖𝑣𝑒𝑛 𝑔𝑒𝑎𝑟
𝑁𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑡𝑒𝑒𝑡ℎ 𝑜𝑛 𝐷𝑟𝑖𝑣𝑒𝑟 𝑔𝑒𝑎𝑟
=
1
2
GEAR TRAIN 4:
𝐺𝑒𝑎𝑟 𝑅𝑎𝑡𝑖𝑜 =
=
20
80
𝑁𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑡𝑒𝑒𝑡ℎ 𝑜𝑛 𝐷𝑟𝑖𝑣𝑒𝑛 𝑔𝑒𝑎𝑟
𝑁𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑡𝑒𝑒𝑡ℎ 𝑜𝑛 𝐷𝑟𝑖𝑣𝑒𝑟 𝑔𝑒𝑎𝑟
=
1
4
Explain concept: CAR TRANSMISSION:Often, a transmission will have multiple
gear ratios (or simply "gears"), with the ability to switch between them as speed
varies. This switching may be done manually (by the operator), or automatically.
Directional (forward and reverse) control may also be provided. Single-ratio
transmissions also exist, which simply change the speed and torque (and sometimes
direction) of motor output.
BEVEL GEARS
a) MITER GEARS:
A bevel gear is shaped like a right circular cone with most of its tip cut off.
When two bevel gears mesh, their imaginary vertices must occupy the same point. Their shaft axes
also intersect at this point, forming an arbitrary non-straight angle between the shafts.
Bevel gears with equal numbers of teeth and shaft axes at 90˚ are called miter gears.
Designed to transmit motion & power between right angle shafts (90°, intersecting), which rotates in
the opposite direction
Bevel gears are durable and ideal for high load applications.
Plastic, brass, steel, & aluminium are the materials generally used for manufacturing miter gears.
28
USES:
Hand drills, printers, automobiles, locomotives, elevators & blowers are just a few everyday machines
where bevel gears are used.
Bevel gears are also used in machine tools, material handlers, conveyors, cooling towers, power
plants, rotorcrafts & marine applications
b) ANGULAR BEVEL GEARS:
Bevel gear is characterized as gear of conical form designed to operate on intersecting axes. These
gears allow transmission of power around corners so to speak as their shafts intersect. Most
commonly the shafts will intersect at a 90˚ angle. Straight bevel gears have teeth that are straight,
radially from the gears centre point. Angular bevel gear is characterized as a gear in which the
axes are not at right angles.
The same general rule applies to bevel gears:
Low gear ratio
High gear ratio
= more speed
= less speed
= less force
= more force
Rack – and – pinion gears:
A rack and pinion is a type of linear actuator that comprises a pair of gears which convert rotational
motion into linear motion. A circular gear called "the pinion" engages teeth on a linear "gear" bar
called "the rack"; rotational motion applied to the pinion causes the rack to move, thereby translating
the rotational motion of the pinion into the linear motion of the rack.
A typical example of this is the rack-and-pinion that operates electrical gate motors. The rack is
attached to the base of the gate that runs on a track, while the pinion protrudes from the gate motor.
When the pinion is rotated by the motor, it causes the rack to move:
Four possible uses for a rack-and-pinion gear system: (p.67)
1
2
3
4
steering mechanism of cars or other wheeled, steered vehicles
Electrical sliding gates
Automated garage doors
Tank wheels
WORM GEARS:
Worm gears are used when large gear reductions are needed. It is common for
worm gears to have reductions of 20:1, and even up to 300:1 or greater.
Many worm gears have an interesting property that no other gear set has: the worm
can easily turn the gear, but the gear cannot turn the worm. This is because the
angle on the worm is so shallow that when the gear tries to spin it, the friction
between the gear and the worm holds the worm in place.
This feature is useful for machines such as conveyor systems, in which the locking
feature can act as a brake for the conveyor when the motor is not turning.
29
GEARES around the HOUSE: Investigation (p.70)
Name
Picture
Main
purpose
Opening cans
Gear System present
Spur gears
mixing
Bevel gears
Opening tight caps
Rack-and-pinion
Loosening / tightening
bolts
Worm gear
Clamping to hold
Worm gear
Loosening / tightening
bolts
Ratchet and pawl
Can opener
Egg beater
Strap spanner for
bottles
Pipe wrench
Bench Vise Grip
Ratchet spanner
Find another house-hold item that makes use of one of the gear systems we looked at. Learners to
complete table as per own selection – check accuracy.
ITEM:
GEAR SYSTEM PRESENT:
PICTURE / DRAWING:
EVALUATION EXERCISE (p.71)
The report is to be approximately 50 words per item and assessed by using the
following rubric:
A Holistic Rubric for Assessing Writing in Technical Reports
Score
8 – 10
5–7
3–4
0–2
Descriptor
Writing shows superior abilities in writing in English, with correct grammar,
spelling, sentence structure, and the ability to put thoughts together in a
coherent manner with personal insights that indicate an ability to see the big
picture.
Writing is acceptable. Grammar, spelling, and sentence structure are correct
but style is rudimentary. Writer is not able to show that he/she is able to see
the big picture.
Writing is barely acceptable. Grammar, spelling and sentence structure are
almost free from error to make sense of the writing, but the reader must
make an effort to arrive at the proper interpretation.
Writing is primitive and not acceptable for grade 9 level. The given criteria
were not successfully addressed.
30
ARTISTIC DRAWING
(p.72)
Learner’s own drawings – pay attention to detail, scale, vanishing point
YOUR 3-D NAME DESIGN
Using single vanishing point perspective.
Adding fine detail such as wood-grain, colour and shadows.
The shading and colouring will contribute to the “feeling”
artistic TOY sketch:
Using single vanishing point perspective.
Adding fine detail such as wood-grain, colour and shadows.
The shading and colouring will contribute to the “feeling”
MINI-PAT:
Integrated Systems:
(p.74)
A design brief has to be written up
Two sketch drawings of possible designs must be done.
A model is required.
Instructions must be added so that anyone will be able to operate the model.
The following rubric is used to assess the project:
Skill
Investigation
skills
Design Skills
Making skills
Communicatio
n Skills
Exceptional
8 - 10
Appropriate model
chosen showing
insight, intricate
Good
6-8
Model chosen
simple, but
appropriate
Adequate
4-5
Model works, but
not entirely
appropriate
Well-thought out
design, interesting
concept.
Design is good,
but lacks
initiative.
Design sketches of
high quality
Design sketches
need attention.
Design addresses
some of the
investigation
criteria.
Design sketches
not neat or clear.
Very neat, well laid
out, a pleasure to
work with.
Prototype working
perfectly.
Ideas, design and
model are well
presented and
class’s attention
held through-out
presentation.
Neat, but not
interesting.
Not neat or badly
constructed.
Prototype working
perfectly.
Ideas, design and
model not as well
presented, but
class seems
interested in
prototype.
Some flaws in
prototype evident.
Ideas / design /
model not well
presented. Class
seems
disinterested in
prototype.
Mark / 50
31
Disappointing
<4
Model not
appropriate or fails
the investigation
criteria
Design lacking in
fulfilling
investigation
criteria.
Design sketches
not neat or
absent.
Sloppy or poorly
constructed.
Prototype fails.
Ideas / design /
model absent.
Presentation fails.
MODULE 3:
ELECTRICAL / ELECTRONIC SYSTEMS
3.1.
Revision: Electrical systems and control – component symbols
Electricity is related to charges, and both electrons and protons carry a charge. The amount of the
charge is the same for each electrons and protons, but opposite in sign. Electrons carry a negative
charge while protons carry positive charge. The objects around us contain billions and billions of
atoms, and each atom contains a fixed number of protons and electrons, according to the atom’s
atomic number. The protons are located in the center of the atom, concentrated in a small area called
the nucleus. The electrons are in motion outside of the nucleus in orbitals. The protons are basically
trapped inside the nucleus and cannot escape the nucleus. As a result, it is moving electrons that are
primarily responsible for the flow of electricity.
Current is a measure of the amount of charge transferred over a period of time. Current is a flow of
electrons, or individual negative charges. When charge flows, it carries energy that can be used to do
work.
There are two main kinds of electric current, direct current (DC) and alternating current (AC). They
are easy to remember. Direct current is a flow of charge always in one direction. Alternating current
is a flow of charge back and forth, changing its direction many times in one second. Batteries produce
DC current, while the outlets in our homes use AC current.
The symbol "V" is used to represent potential difference. Potential difference is a measure of the
amount of work done in moving a charge between two points, divided by the size of the charge. The
potential difference is measured in volts, and potential is commonly referred to as voltage. "I" is the
symbol for current. Current is measured in amperes. "R" is the symbol for the resistance of the
system. and resistance is measured in ohms. We use the symbol Ω to abbreviate ohms.
The relationship between V, I and R is known as Ohm’s law:
The amount of electric current through a metal conductor, at a constant temperature, in a circuit is
proportional to the voltage across the conductor. Mathematically, Ohm’s Law is written: V = I × R
This relationship can be illustrated as follows:
V= I×R
I=
V
R
R=
V
I
There are two requirements that must be met in order to establish an electric circuit.
The requirements are:


There must be an energy supply capable doing work on charge to move it from a low
energy location to a high energy location and thus establish an electric potential difference
across the two ends of the external circuit.
There must be a closed conducting loop in the external circuit that stretches from the high
potential, positive terminal to the low potential, negative terminal.
32
INTERESTING QUESTION: (p.77)_
In the movie Tango and Cash, directed by Andrey Konchalovskiy, with Sylvester
Stallone, Kurt Russell, Teri Hatcher, Jack Palance, two cops are framed and must
clear their names. They escape from a prison by jumping off the top of a tall wall
through the air and onto a high-voltage power line. Before the jump, Stallone
objects to the idea, telling Russell "We're going to fry." Russell responds with "You
didn't take high school Physics did you. As long as you're only touching one wire and
you're feet aren't touching the ground, you don't get electrocuted."
Is this true?
Motivate your answer
YES
NO
fully:
Obviously, there was no path to ground through them. In order to get a shock, current
has to flow through your body. Merely contacting a voltage source will not necessarily
shock you. Linemen make use of this fact when repairing live high-voltage transmission
lines. As long as there is no path to ground through the lineman's body, he can safely
hold on to a wire energized with 750,000 V or more.
If you answered “Yes”, you would be absolutely right!
In order for there to be a sustained flow of charge from one location to another, there must be a
difference in electric potential. In this case, there would be a momentary flow of charge between the
wire and the actor until they reach the same electric potential. Once at the same potential, charge
flow would cease and there would be no electrocution. However, if the actor's feet touched the
ground (an electric potential of 0 ) or another wire of a different potential, then there would be a
sustained charge flow which likely would lead to electrocution.
The direction of an electric current is by convention the direction in which a positive charge would
move. Thus, the current in the external circuit is directed away from the positive terminal and toward
the negative terminal of the battery.
Electric circuits
33
SERIES / PARALLEL
Emphasize the following:
COMPONENT:
...connected in series....
...connected in parallel....
Cells
produce a greater current that
would cause a light bulb to burn
more brightly.
The total potential difference equals
the sum of the individual potential
differences.
produce the same current as each
individual cell, but allows the light bulb
to burn for an extended time. The
potential difference of the connected
cells equals the potential difference of
each individual cell.
cause the total resistance of the
circuit to increase.
identical resistors or light bulbs will
divide the current equally amongst
different branches
Resistors
and
the voltmeter reading across the
combination equals the sum of the
voltmeter reading across each
resistor - divide up the total
potential difference (voltage
dividers).
the voltmeter reading across the
combination is the same as the
voltmeter reading across each
individual resistor.
Light bulbs
current is equal at all points
through-out a series circuit.
𝑅𝑇𝑜𝑡𝑎𝑙 = 𝑟1 + 𝑟2 + … ….
Each resistor has the total current
flowing through it. The total
resistance equals the sum of each
individual resistor.
the currents in each resistor connected
in parallel add up to the main current in
the circuit – resistors in parallel are
therefore called current dividers.
1
1 1
= + + … ….
𝑅𝑇𝑜𝑡𝑎𝑙 𝑟1 𝑟2
Resistor with the highest resistance
carries the smallest current.
The total resistance is smaller than any
of the individual resistors in the
combination.
Where series as well as parallel combinations occur in a circuit, it is easier to first calculate the
resistance of each parallel combination in the circuit and then add these calculations to the other
resistors as would normally be done in a series circuit (we say we “collapse” the parallel resistors first
to be able to treat them as resistors in series).
34
The electrical circuits in our homes:
Questions (p.80)
Do you think that the electrical appliances in your home are connected in series or in
parallel? (Mark the correct option with a √)
Series
Parallel
√
Why is this method of connection ideal?
At home all your appliances are connected in parallel with each other. This means they all
get the full mains voltage and you can turn on your TV without having to turn on your
microwave as well. The electric cables in your house contain three wires. We'll ignore the
earth for the moment and just concentrate on two of them: the live and the neutral. In Europe
the live is brown and the neutral is blue. In the US live can be black, red or yellow; and
neutral tends to be white or white with yellow stripes.
There is a voltage between the live and neutral because they are indirectly connected to a
power plant. Each electric socket in your home is connected to the live and the neutral. The
metal pins of a plug make an electrical connection with the socket. A lead, again with live
and neutral wires, connects the plug to your appliance.
Each appliance has its own connection between live and neutral so each appliance can be
switched separately and has the whole live voltage across it.
Even though all the appliances in your home are connected across the same voltage, they'll all
draw different currents. An electric oven transfers energy quickly so the current drawn by
that will be big. The TV transfers energy quite slowly so the current drawn by that will be
quite small.
Do you think christmas tree lights are connected in series or parallel?
Series
Parallel
√
Motivate your answer:
If one bulb “blows’ – all the lights are dead.
35
Sour Cell-power!
You can make an electric cell to supply low-voltage power
for toys by using a lemon!
The lemon battery is called a voltaic battery, which changes
chemical energy into electrical energy. The battery is made
up of two different metals (the zinc nail or zinc paper clip
and the copper coin or drawing pin). These are called
electrodes, which are the parts of a battery where electric
current enters or leaves the battery. The electrodes are
placed in a liquid containing an electrolyte, which is a
solution that can conduct electricity. In a solution of water
and an electrolyte, like the acid in the lemon, an excess of
electrons collects on one end of the electrodes. At the same time, electrons are lost from the other
electrode.
Wiring a plug:
1. Open the plug by either unscrewing the screw on the base
(generally a star / Phillips head) or unclipping the plug if it is a clip
plug.
2. Once the plug is open you will see 3 smaller screws, you can undo
these screws enough for the cable to be placed inside.
3. Strip the protective shielding on the cable to show the inside smaller
cables. (You should now see a brown, blue and a yellow & green
(combined))
4. Remove a section off the top of the 3 cables to expose the copper
wire, enough copper wire needs to be exposed to place through the
small holes where the screws we loosened earlier.
5. You will now place the cables in the necessary holes and tighten the
screws to hold them in place.
CIRCUIT DIAGRAMS:
Look at the following circuit diagram:
A few things to note:
1.
The flow of charge is from + to –
terminal of battery.
2.
The voltmeter is connected in parallel.
3.
The ammeter is connected in series
4.
The battery is a series of cells
36
Connecting resistors into a circuit:
When resistors are connected in series to a circuit, we increase the resistance to the flow of
current. There is only one path that the current can flow down and the current is the same at
all places in the series circuit. Take a look at the diagram below:
On the left there is a circuit with a single resistor and a battery.
No matter where we measure the current, it is the same in a series circuit.
On the right, we have added a second resistor in series to the circuit.
The total resistance of the circuit has increased and you can see from the reading on the
ammeter that the current in the circuit has decreased. When resistors are connected in
parallel, we create more paths along which current can flow. By doing this we decrease the
total resistance of the circuit
A resistor is a physical component of a circuit that has resistance. Resistance is defined as the ratio of
the voltage and the current through a physical component, as defined by Ohm's law.
When resistors are added in series to the circuit, the total resistance increases. The total resistance
is:
𝑅𝑇𝑜𝑡𝑎𝑙 = 𝑟1 + 𝑟2 + … ….
When resistors are added in parallel to the circuit the total resistance decreases. The total resistance
is:
1
1 1
= + + … ….
𝑅𝑇𝑜𝑡𝑎𝑙 𝑟1 𝑟2
where R is the total resistance and r1, r2, etc. is the resistance of the individual resistors.
Assignment (p.84)
The following circuit diagram shows the following components:
a) 2 cells in parallel
b) an open switch
c) 2 resistors in parallel
d) an ammeter measuring total current
e) a voltmeter measuring potential difference across one of the parallel resistors
37
1.
What effect would the two cells in parallel have on the current in the circuit?
Same current as for single cell, but lasts twice as long
2.
If each of the resistors has a resistance of 2Ω, what would the combined the resistance of the
two resistors be?
1
𝑅𝑇𝑜𝑡𝑎𝑙
3.
=
1 1 1 1
+ = + = 1Ω
𝑟1 𝑟2 2 2
If each cell has a potential difference of 1,5V, what reading would show on the ammeter
upon closing the switch?
𝐼=
𝑉 1,5
=
= 1,5𝐴
𝑅
1
Three identical light bulbs A, B and C are connected in an electric circuit as shown in the diagram
below:
1.
Write up a short comparison on the brightness of the three light bulbs in the circuit:
A is twice as bright as other two.
B and C are equally dim.
2.
Describe the brightness of the three different bulbs after switch S has been opened.
C will not be working
A and B are equally bright, as bright as A was in question 1.
3.
How do the currents in bulbs A and B change when switch S is opened?
Tick the correct answer:
a
b
c
d
4.
Current in A
decreases
decreases
increases
increases
Current in B
increases
decreases
increases
decreases
Correct option?
A stays same, B
increases in brightness.
Match the following terms into pairs: SERIES; VOLTAGE DIVIDERS; PARALLEL; CURRENT
DIVIDERS:
series
parallel
=
=
38
Voltage dividers
Current dividers
ACTIVITY: Wiring of a house and electrical calculations (p.86)
You are going to calculate the resistance and current strengths in the wiring in certain rooms of a
four-room house by drawing a schematic house plan to help you.
Your house has:
 four rooms
 a 220V power source
 a Distribution board (circuit board) in the kitchen
 a light in each room, all connected in parallel, with a total resistance of 24Ω
 a stove in the kitchen, which needs a current strength of 8A to work
Draw a simple circuit diagram that will represent the wiring of this house:
1.
2.
3.
Calculate the strength of the current that will make the lights burn:
𝐼=
𝑉 220
=
= 2,29 𝐴
𝑅
96
𝑅=
𝑉 220
=
= 27,5 Ω
𝐼
8
What is the resistance of the stove?
Do you think the heat produced by the stove is caused by its high resistance?
Yes
39
Draw up your own circuit diagram with the following components:
a)
b)
c)
d)
e)
f)
g)
Four cells (each 1,5V) connected in series with a voltmeter (V1) connected across it
A closed switch in series with the battery
An ammeter (A1) in the main circuit,
Two resistors in series, each of magnitude 2Ω
A combination of three resistors connected in parallel, each measuring 2Ω
A voltmeter across the parallel combination of resistors (V2)
An ammeter (A2) in series with one of the resistors in the parallel combination
V
V
A
A
V
1.
Calculate the reading on V1.
𝑉 = 4 × 1,5 = 6𝑉
2.
Calculate the total resistance of the resistors in the parallel combination.
1 1 1 1 3
= + + =
𝑅 2 2 2 2
𝑅=
3.
2
3
Calculate the total resistance in the circuit:
𝑅 = 2+2+
4.
Ω
Calculate the reading on Ammeter A1
𝐼=
𝑉
𝑅
=
6
4
2
3
9
= A
7
40
2
2
=4
3
3
5.
What would be the reading on A2?
𝐼=
6.
3
𝐴
7
Calculate the reading on V2.
9
27
𝑉= 7 =
𝑉
2 98
4
3
The resistors used in industry are colour-coded to define their magnitudes:
Use the colour guide above to determine the size of
this resistor:
104x0,01 = 1,04 Ω
41
Switches:
In circuits, a switch is an electrical component that can break an electrical circuit, interrupting the
current or diverting it from one conductor to another.
The most familiar form of switch is a manually operated electromechanical device with one or more
sets of electrical contacts. Each set of contacts can be in one of two states: either "closed" meaning
the contacts are touching and electricity can flow between them, or "open", meaning the contacts are
separated and the switch is non-conducting.
Type
Circuit symbol
Picture example
Push / SPST Momentary
SPST
(Single Pole, Single
Throw)
SPDT
DPDT
Complete the following table by filling in two uses for each switch in the space provided:
Any two relevant examples to be provided by learners
Explain The concept: Diodes and LED
A light-emitting diode (LED) is a semiconductor light source. LEDs are used as indicator lamps in
many devices and are increasingly used for other lighting. Early LEDs emitted low-intensity red light,
but modern versions are available across the visible, ultraviolet and infrared wavelengths, with very
high brightness. When a light-emitting diode is switched on, electrons are able to recombine with
electron holes within the device, releasing energy in the form of photons. This effect is called
electroluminescence and the colour of the light (corresponding to the energy of the photon) is
determined by the energy gap of the semiconductor. LEDs are often small in area (less than 1 mm2),
and integrated optical components may be used to shape its radiation pattern. LEDs present many
advantages over incandescent light sources including lower energy consumption, longer lifetime,
improved robustness, smaller size, and faster switching. LEDs powerful enough for room lighting are
relatively expensive and require more precise current and heat management than compact
fluorescent lamp sources of comparable output.
Light-emitting diodes are used in applications as diverse as replacements for aviation lighting,
automotive lighting (particularly brake lamps, turn signals and indicators) as well as in traffic signals.
LEDs have allowed new text, video displays, and sensors to be developed, while their high switching
rates are also useful in advanced communications technology. Infrared LEDs are also used in the
remote control units of many commercial products including televisions, DVD players, and other
domestic appliances.
42
Assignment (p.91)
Can you name four appliances / products in your home that contain a light-emitting diode?
1
2
3
4
LED downlighters
computers
Television
Hi-fi
If these LEDs are in fact more energy-efficient than conventional lighting, why are they not more
widely used?
Expensive option
Not as bright
Do not emit light in all directions
Linear phosphorescent lights have longer life span
Research question: What is the main difference between a PLASMA TV and a LED TV?
Of the two types of sets, LCD technology is the most familiar to the average consumer: it’s
the exact same display technology that is used in most flat screen desktop and laptop
monitors. The benefits are a slim profile, ideal for wall mounting and significantly lighter and
less bulky than the old CRT (cathode ray tube) televisions. LCDs also use less power than
plasma displays, minimize glare and are not susceptible to burn-in… the elephant in the room
when plasma displays are discussed. Burn-in is what happens to an HDTV when an element
of an image is displayed for a prolonged period of time in a single area of the display. Burnin results in a ghostly afterimage of that element appearing on the display for a long time
after the element itself is gone. Both LCDs and plasma screen televisions are susceptible to
burn-in, but it is relatively rare on LCDs, while plasma displays are notorious for it. Finally,
LCDs support a far larger spectrum of screen sizes than plasma displays. But the benefits of
LCD come at a cost, and that cost is colour depth and black qualities. Compared to a plasma
display, an LCD could have (relatively) muddied colours and grayish blacks. A plasma
display is up to four times more accurate in reproducing colour, and produces deep, true
blacks with contrast ratios up to 1:1,000,000. Plasma displays also afford users a wider
viewing angle of their television, maxing out at almost 180 degrees, and their higher refresh
rates can virtually eliminate motion blur. If it wasn’t for plasma displays propensity for burnin, they’d be easy to recommend over an LCD display: the technology is simply better at
reproducing colour and giving off luridly deep blacks than LCDs. But while plasma displays
have come a long way in reducing burn-in, it is still a danger. They are also marginally
bulkier than LCD displays. Here’s what it boils down to: Buy a plasma display if you want
the best colour, deepest blacks, widest viewing angle and highest refresh rates, in a set
between 32-inches and 62-inches diagonally. Plasma displays are also perfect for watching
sports or action movies, and they are marginally cheaper than equivalent LCD displays.
LCDs, on the other hand, are the best choice for people who need to protect their display
against burn-in. Gamers, for example, should consider an LCD display to prevent the headsup display (HUD) elements of their video games from becoming a constant ghostly presence
on their screens.
Define the following terms:
HDTV
LCD
LED
High definition television
Liquid crystal display
Light emitting diode
43
Explain concept: SENSORS
A sensor (also called detector) is a device that measures a physical quantity and converts it into a
signal that can be read by an observer or by an instrument.
More and more cars are fitted with “park-assist”. This is just one type of sensor where A proximity
sensor is used. This is a sensor able to detect the presence of nearby objects without any physical
contact. A proximity sensor often emits an electromagnetic or electrostatic field, or a beam of
electromagnetic radiation (infrared, for instance), and looks for changes in the field or return signal.
Various types of these sensors are available to address a variety of different uses.
Type
1
2
3
4
LDR
(Light
Dependent
Resistor)
Thermistor
Touch or
moisture
detector
Capacitors
Function / Use
As its name implies, the Light Dependant Resistor (LDR) is made from a
piece of exposed semiconductor material such as cadmium sulphide that
changes its electrical resistance from several thousand Ohms in the dark to
only a few hundred Ohms when light falls upon it by creating hole-electron
pairs in the material. The net effect is an improvement in its conductivity
with a decrease in resistance for an increase in illumination. Also, photoresistive cells have a long response time requiring many seconds to
respond to a change in the light intensity. One simple use of a Light
Dependant Resistor, is as a light sensitive switch.
Thermistors are thermally sensitive resistors and have, according to type,
a negative (NTC), or positive (PTC) resistance/temperature coefficient.
Thermistors can be custom-designed to match the electrical and thermal
characteristics of gauges and probe housings. Designed for driving
automotive coolant temperature gauges, the composite sensor resistance
is virtually constant over a specified range, which results in a steady centre
dial gauge reading during normal engine operation. Hot and cold zone
sensitivity are retained, so that motorists are warned of abnormal
conditions.
These sensors are placed inside products where trace amounts of moisture
could damage the electronic circuits. Some iPhone owners are claiming
that exercise, while good for you, may break your Apple device. Of course,
as with most electronic devices, significant moisture can ruin Apple's
iPhone, iPod Touch, and iPod. But now, some are saying that water
damage may occur during activities as mundane as going for a jog!
In a way, a capacitor is a little like a battery. Although they work in
completely different ways, capacitors and batteries both store electrical
energy. A battery has two terminals. Inside the battery, chemical reactions
release electrons at one terminal and absorb electrons at the other
terminal. A capacitor is much simpler than a battery, as it can't produce
new electrons -- it only stores them. Different types of capacitors exists
with uses such as: radio tuning circuits; timer circuits like clocks, alarms
and counters ; high frequency purposes like antennas, X-ray and MRI
machines; Powers electric and hybrid cars.
44
ACTIVITY: (p.93) Electronic systems and control practical
Show learners how to build - http://www.instructables.com/id/Build-a-Simple-Circuitfrom-a-Pizza-Box-No-Solder/
COMPONENTS:
LED
Buzzer
1 kΩ Resistor
470 Ω Resistor
NPN transistor
1 000 µF Capacitor
4 × 1,5 V cells
Thermistor
Switch
LDR
Variable resistor
Draw and build the following circuits:
1.
LED; 470 Ω Resistor; Switch; 4,5 V series battery:
2.
LDR; Buzzer; 3 V series battery:
learners to draw up circuit diagrams using correct components.
Lateral extension: show them: http://circuiteasy.com/automatic-street-light/
buzzer
3.
LDR
NPN Transistor; Buzzer; Thermistor; Variable resistor; 1 kΩ Resistor; 6 v
series battery:
45
NPN transistor
buzzer
variable resistor
or
resistor
battery
thermistor
4.
6 V series battery; LED; 470 Ω Resistor; 1 000 µF Capacitor; Switch:
battery
resistor
capacitor
switch
46
PAT (Practical Assessment Task): (p.95)
INNOVATION: Electronic systems and control
Check for the following skills:
Skill:
1
2
3
4
Investigation skills
Design skills
Production skills
Communication skills
Description:
Investigate the situation and the nature of the need so that an appropriate
circuit can be chosen to solve the problem, need or want given in the
scenario.
A given circuit must be incorporated into the design of a device that will use
the electronics to address the problem, need or want.
Each learner writes his/her suggestion for the design with specifications &
constraints.
Each learner draws the circuit diagram. Each learner produces a sketch in 3D
showing the device that will use the electronic circuit.
Teams meet and examine the individual suggestions to decide on a final
solution.
Plans: working drawings
The learners produce plans for their device/model/prototype using first angle
orthographic projection. The plans should include a 3D “assembly” drawing
in exploded view showing how the model fits together. Each team member
draws a working drawing of the design OR an aspect of the design. Make:
device /prototype/working model
The model must showcase a viable solution to the problem. It should be to
scale and neat, and show intelligent use of available materials.
Team presentations:
Each team is given five minutes to present their solution in the form of
sketches, artistic impressions of the solution, working drawings/plans,
costing and their model.
An example of a simple electronic educational game:
Slide the attached magnetic wand across
the acrylic cover to guide the colourful balls
around the board. Fill each numbered hole
with the correct number of balls. 12" x 9" x
7.5". Great for ages 3 and above.
47
The following rubric can be used to assess the PAT assignment:
Skill
Investigation
skills
Design Skills
Making skills
Communicatio
n Skills
Exceptiona
l
8 - 10
Appropriate
circuit
chosen
showing
insight,
intricate
Well-thought
out design,
interesting
concept.
Good
6-8
Adequate
4-5
Circuit
chosen
simple, but
appropriat
e
Circuit
works, but
not entirely
appropriate
Design is
good, but
lacks
initiative.
Design
addresses
some of the
investigatio
n criteria.
Design
Design
Design
sketches of
sketches
sketches not
high quality
need
neat or
attention.
clear.
Very neat,
Neat, but
Not neat or
well laid out, not
badly
a pleasure to interesting. constructed.
work with.
Prototype
Prototype
Some flaws
working
working
in prototype
perfectly.
perfectly.
evident.
Ideas,
Ideas,
Ideas /
design and
design and design /
model are
model not model not
well
as well
well
presented
presented, presented.
and class’s
but class
Class seems
attention
seems
disintereste
held
interested
d in
through-out in
prototype.
presentation prototype.
.
Mark / 50
48
Disappointin
g
<4
Circuit not
appropriate or
fails the
investigation
criteria
Design lacking
in fulfilling
investigation
criteria.
Design
sketches not
neat or absent.
Unneat or
poorly
constructed.
Prototype fails.
Ideas / design
/ model
absent.
Presentation
fails.
Explain concepts: SHORT CIRCUITS and CIRCUIT BREAKERS
A short circuit is an accidental path of low resistance which passes an abnormally
high amount of current. A short circuit exists whenever the resistance of a circuit or
the resistance of a part of a circuit drops in value to almost zero ohms. A short often
occurs as a result of improper wiring or broken insulation.
A circuit breaker is an essential device in any electrical circuit as it is one of the most
important safety mechanisms in your home. Whenever electrical wiring in a building
has too much current flowing through it, these simple components cut the power
until somebody can fix the problem. Without circuit breakers (or the alternative,
fuses), household electricity would be impractical because of the potential for fires
and other mayhem resulting from simple wiring problems and equipment failures.
Power Plants in South Africa
Eskom supplies about 95% of South Africa's electricity and approximately 45% of
Africa's.
COAL-FIRED POWER STATIONS
Name two major disadvantages that you think a coal-fired power station holds for
South Africa?
The disadvantages of coal power are;
1. It is non-renewable and it is causing global warming.
2. Although it is now cheap, if the coal continues to be used in such a way, it
will soon be very expensive.
3. Burning a fossil fuel produces carbon dioxide, which contributes to the
greenhouse effect, warming the Earth.
4. Burning coal produces more carbon dioxide than burning oil or gas.
5. Mining coal can be difficult and dangerous. Strip mining destroys large areas
of the landscape.
6. Coal-fired power stations need huge amounts of fuel, which means trainloads of coal almost constantly. In order to cope with changing demands for
power, the station needs reserves. This means covering a large area of
countryside next to the power station with piles of coal, which destroys plants
and ruins landscapes.
49
NEW DEVELOPMENTS:
Eskom has started work on two new coal-fired power stations, and is considering bids from two
overseas companies to build a new conventional nuclear power station.
Eskom also plans to reopen three power stations that were mothballed in the 1990s, build two opencycle gas turbines that will produce power by the end of 2009, and complete a hydro scheme in the
Drakensberg in KwaZulu-Natal.
NUCLEAR POWER
South Africa's main coal reserves are concentrated in Mpumalanga in the northeast, while much of
the electricity load is on the coast near Cape Town and Durban.
Moving either coal or electricity over long distances is inefficient, so it was decided in the mid-1970s
to build some 1800 MW of nuclear capacity at Koeberg near Cape Town.




South Africa has two nuclear reactors generating 5% of its electricity.
South Africa's first commercial nuclear power reactor began operating in 1984.
Government commitment to the future of nuclear energy is strong, with firm plans for further
9600 MW in the next decade, but financial constraints are severe.
Construction of a demonstration Pebble Bed Modular Reactor has been cancelled.
The Koeberg plant was built by Framatome (now Areva) and commissioned in 1984. It is owned and
operated by Eskom and has twin 900 MWe (940 MW gross) pressurised water reactors (PWRs), the
same as those providing most of France's electricity. While there had been no intention to build
further power stations of this type, the government announced early in 2006 that it was considering
building a further conventional nuclear plant, possibly at Koeberg, to boost supplies in the Cape
province.
The Pebble Bed Modular Reactor (PBMR) is a particular design of pebble bed reactor under
development by South African company PBMR (Pty) Ltd since 1994. The project entails the
construction of a demonstration power plant at Koeberg near Cape Town (now postponed
indefinitely) and a fuel plant at Pelindaba near Pretoria.
Although it is not the only gas-cooled high-temperature reactor currently being developed in the
world, the South African project is internationally regarded as the leader in the global power
generation field. The PBMR is characterised by inherently safe features, which mean that no human
error or equipment failure can cause an accident that would harm the public.
ACTIVITY: Mind-map (p.100)
Not to be assessed – learners to include all important concepts covered.
Letter to Government regarding “greener” power: (p.101)
A letter of 120 – 150 words to our government in which alternatives to coal-fired
power stations are hightlighted.
50
The following rubric can be used to assess:
Criteria
Areas
A
B
C
Format
__includes typed
final, prewrite or
outline, marked
draft, & Works
Cited in prescribed
format
__includes
typed final, prewrit
e or outline, marked
draft, & Works Cited
- some (minor)
errors in prescribed
format
__ missing
prewrite/outline,
draft or Works
Cited; insufficient
editing of draft or
outline; numerous
errors in format
Underst
anding
of
literatur
e/ texts
Idea
Develop
ment
__ writing shows
unusual insight
understanding
__writing shows
strong, clear
understanding
__ presents fresh
thesis in an
original manner
while displaying
unusual insight
Text
Support
__more than
adequate/correct
MLA format;
smooth embedding
__ strong,
interesting; clear
beg/middle/end;
strong thesis that
is marked on draft
__ presents an
effective thesis
and development
using a consistent,
careful manner
incorporating exam
ples
__adequate/some
errors in MLA
format; generally
smooth embedding
__ organized; clear
beg/middle/end;
clear thesis that is
marked on draft
__includes
typed final,
prewrite/ outline,
draft, & Works
Cited, but
insufficient editing of
draft; several errors
in prescribed format
__writing shows
adequate
understanding but
may be too general
or superficial
__ presents a clearly
defined thesis, but
the development is
too general or may
not be marked by
independent thought
__inadequate/sever
al errors in MLA
format; some faulty
embedding
__ somewhat
organized; attempt
at beg/middle/end;
thesis is weak or
unclear - not
marked on draft
__ appropriate but
not specific or vivid;
weak "voice" __
weak attempt to
limit use of 1st and
2nd person & "to be"
verbs
__ sometimes
incorrect & lacks
variety
__inadequate/numer
ous errors in MLA
format; ineffective
embedding
__ no attempt at
organization; lacks
clear beg/middle/
end; thesis lacking
or inappropriate not marked on draft
__ simple/vague;
appears to lack
"voice" _excessive
use of 1st and 2nd
person & "to be"
verbs
__ many not smooth
& some errors in
usage; many not
marked on draft
__ several errors;
requires additional
proofreading
__ not used &/or
frequent errors in
usage; many not
marked on draft
__ numerous errors;
appears not to have
been proofread
Organiz
ational
Pattern
Word
Choice
_ fresh/vigorous;
contributes to
"voice" __ very
limited use of 1st
and 2nd person &
"to be" verbs
__vivid/interesting;
attempt to establish
"voice" __ limited
use of 1st and 2nd
person & "to be"
verbs
Sentenc
e
Structur
e
Transiti
onal
Devices
__ correct/varied
__ correct, but lacks
variety
__smooth &
effective; marked
on draft
Languag
e
Mechani
cs
__ very few (if
any) errors; very
well proofread
__ somewhat
smooth & generally
effective; most
marked on draft
__ few errors;
generally well
proofread
51
D
__writing shows
little or no
understanding of
text
__ poorly defined or
inconsistent
development
of thesis that
displays little insight
__ frequent errors &
lacks variety
MODULE 4: Processing:
CONTENTS
1. Research assignment
 Recipes and the use of gelatine
2. Case



studies
Investigation – Components of an existing recipe
Properties of gelatine 1 – jelly, marshmallows, gums
Properties of gelatine 2 – Information “What is Gelatine?”
3. Assignments
 Recipe construction
 Simple recipe construction
 Classification of products
 Factors that influence gelatine
 Measuring procedure and assignment with assessment
4. Project on “A Great Gelatine Dessert”
 Design portfolio:
 Statement of the problem
 Design brief
 Investigation
 Proposal
 Initial ideas
 Research
 Development of chosen idea
 Planning ( working drawings, materials, tools, flowchart)
 Manufacturing/Making
 Testing, Evaluation and improvement
 Marketing
5. Assessment
52
1.4. Recipe Construction.
Butter Biscuits
Ingredients
250g soft butter
125ml castor sugar
125 ml condensed milk
375g cake flour
10ml baking powder
0,5ml table salt
5ml vanilla essence
Method
1.
2.
3.
4.
5.
Cream the butter and sugar to a light fluffy consistency.
Stir in the condensed milk and mix well.
Sieve and add the dry ingredients.
Add the vanilla essence.
Roll pieces of dough into small balls and place onto a
greased baking sheet.
6. Flatten the biscuit by placing a pecan nut on top of each
biscuit.
7. Bake in a pre-heated oven at 180˚C for 15minutes till
golden brown.
8. Place the biscuits on a cooling rack till cool.
Additional Information
1. Substitute a walnut for the pecan nut to place onto the
biscuit.
53
Research Assignment
Manufacturing process of gelatine
Gelatine is a product obtained by the hydrolyzing of certain connective tissues of
animals. The process of gelatine manufacture involves 3 basic steps. 1) The raw
material is treated to separate collagen from non-collagenous components. 2) The
purified collagen is converted into gelatine. 3) The gelatine is refined and recovered
in dry form.
Characteristics of a good quality gelatine.
Gelatine for food use must meet certain standards of quality. Satisfactory edible
gelatine should have: Little odour, taste, or colour, reasonable gel strength,
thickness and stability.
Forms in which gelatine is marketed.
Granular, powder or sheet form, plain or flavoured.
Uses of gelatine
Refer to page 123 and 124 of the learner manual.
Nutritional value of gelatine.
Gelatine is a protein food and is derived from animal sources, yet its protein is of a
low biological value owing to its lack of 4 essential amino acids: tryptophan,
threonine. methionine and isoleucine. Regardless of the quality of the protein, the
amount of gelatine required to form a gel is so small that its nutritional contribution
is of minor importance. It does have the ability in the strengthening of hair and nails
in the body.
Properties of gelatine.
Hydration and swelling.
Gelatine swells or becomes hydrated when soaked in cold water.
Dispersing gelatine.
When the soaked gelatine is heated to 35°C or above, the gelatine completely
disperses to form a colloidal solution or dispersion.
Gelation.
Gelation refers to gel formation or the setting or stiffening of a gelatine dispersion.
This is a gradual process.
Factors which influence the gelation of gelatine mixtures.
Temperature: Different gelatine mixtures set at different temperatures, but all
mixtures require temperatures below the temperature of dispersion, that is below
35°C. The temperatures required for the solidification of a gelatine dispersion vary
from less than10°C to more or less 14°C - 16°C.
Concentration: The concentration of the gelatine used affects the firmness of the gel
as well as the rate of setting.
Acid: Too high a concentration of an acid may prevent gelation or a soft gel may be
formed, even when fairly high concentatio0ns of gelatine is present.
Salts: The gel strength of gelatine dishes is increased when milk is used as a liquid,
Due to the minerals it contains.
Sugar: If moderate quantity of sugar is added to the mixture, the stiffness of the gel
is increased. Excessive sugar weakens the gel and retards the rate of setting.
Enzymes: The enzyme Bromelin in raw pineapple digests or hydrolyses protein.
Unless it destroyed by heat before the pineapple is added to the mixture, Bromelin
54
will break down the gelatine molecules so that they can no longer form a gel. This
results in a gel of poor texture or no gelation taking place.
Time: Gels become stiffer with long standing. It is thus desirable to allow gelatine
mixtures to stand for several hours or overnight at a low temperature in order to
develop maximum stiffness.
Typical gelatine mixtures.
Foams and Sponges.
A gelatine mixture may be beaten to form a foam. The best stage for beating is
when the mixture has the consistency of thin syrup. To form a sponge, whipped egg
white should be added to the gelatine foam.
Bavarian and Spanish Creams.
Fruit pulp and whipped cream may be folded into the sponge to make Bavarian
creams.
Spanish cream is prepared by stirring hydrated gelatine into an egg custard while
the gelatine is warm and then chilling the mixture.
Reversibility of gelatine.
When a gel melts the process for the development of rigidity are reversed, but the
change occurs more slowly than when the gelatine dispersion is cooled. The degree
of these differences varies according to the rate of heating or cooling. The gel may
be melted and solidified many times.
How to use gelatine.
The gelatine granules should be allowed to soften in cold water for a few minutes as
this allows the gelatine to swell and makes dispersion easier. Add the gelatine to the
hot liquid or heat the soaked gelatine over hot water until the gelatine is thoroughly
dispersed. Gelatine does not actually dissolve but forms a colloidal dispersion that
gels when cool. Cool the gelatine when you add it to milk, cream or custards to
prevent curdling due to the acid used when manufacturing gelatine. Never boil
gelatine mixtures as it becomes stringy and prevents gelation. Always add the cold
liquid to the gelatine dispersion and never the hot liquid to the cold dispersion to
prevent the formation of lumps or strings... Add pieces of fruit or vegetables only
when the process of gelation has already started to prevent the ingredients
1.2. Properties of gelatine.
Questions.
Jelly
1. Table jelly is made from fruit.
2. A vegan is a person who does not eat any animal products.
3. One may use any type of fruit except those that contain enzymes that break down
the Gelatin of gelatine.
Marshmallows.
1. The marshmallows made in France were made from the sap of the root from the
marshmallow plant. The marshmallows today are made from gelatine.
2. The most popular flavours of marshmallows are vanilla and strawberry.
3. Any suitable answer.
Gums and Pastilles.
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1. The flavour added to gelatine-based mixtures is added in the form of a syrup
solution from the fruit juices. (Lemon, orange, lime)
2. Gums are smooth outer texture and pastilles have a sugared texture.
3. Gums should be stored and packed in wrappers, in a cool dry place.
Summary report the three sweet types come from the notes on page 113-115 of the
student manual.
1.5. A simple Recipe Construction.
The diagram and the recipe of the product is marked according to the rubric on page
120 of the students manual.
1.6. Classification of products.
The 10 packages need to be sorted into those with gelatine and those without
gelatine. If the product has gelatine then the name of that type of gelatine should
be noted and written down.
Activity: Properties of gelatine 2 – Assess yourself.
1. Collagen – from the inner layers of skin and bone.
2. The gelatine is extracted to from the commercial product by hydrolysis.
3. The forms in which gelatine is processed are granules, powder and sheets.
4. The characteristics of high quality gelatine are: Tasteless, ordourless,
transparent, pale in colour, has gelling, thickening and stabilizing abilities.
5. The gelatine has the ability to thicken and stabilize, therefore can hold the
hair in place.
6. Collagen are proteins found in animals.
7. Hydroysis is a chemical process in which a water molecule is added to a
substance resulting in the split of that substance into two parts.
1.7. Factors that influence gelatine.
Results
1.Set, firm
2. Soft gel
3. Set gel
4. Liquid
5. Very soft gel
6. Set gel
7. Firm gel
Conclusion
No factors influenced the setting of the
gel formation.
Lemon juice is an acid and will cause the
gel to be less firm.
A small amount of sugar causes the gel
to set firmer.
The enzyme in the pineapple Bromelin
prevents the gel formation.
The increased lemon juice prevents the
forming a stiff gel.
The cooking of the pineapple in the tin
killed the enzyme Bromelin therefore it
did not prevent the gelling process.
The calcium and phosphorous salts in the
milk caused the gel to become firm.
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Self-Study Questions.
1. Raw material is treated to separate collagen from non-collagenous
components; Purified collagen is converted into gelatine; Gelatin is refined
and recovered in dry form.
2. Commercial gelatine is used for stiffener, glue and bookbinding industry.
3. In cold water gelatine hydrates and swells; in hot water gelatine completely
disperses into a colloidal solution.
4. The sol is the gelatine solution in liquid form when it absorbs heat and the
gel is the gelatine solution in solid form when heat is removed by putting it
into the refrigerator.
5. A,B,C
6. Excessive sugar weakens the gel and retards the rate of setting.
7. The enzyme Bromelin digests or hydrates the protein gelatine so it can no
longer form a gel.
8. Gels become stiffer with long standing at low temperatures to develop
maximum stiffness, so one could have planned to make the jelly earlier or left
it in the refrigerator overnight for the next day’s use.
9. Bavarian cream – Gelatine, fruit pulp and whipped cream
Spanish cream – Gelatine and warm egg custard
Charlotte – Gelatine, whipped cream and lady fingers
10. The best stage to beat a gelatine mixture to form a foam is when it is the
consistency of thin syrup.
11. To form a sponge of a gelatine mixture one needs to add whipped egg white
to
the gelatine foam.
12. The gelatine may change from a liquid (sol) by removing the heat from the
mixture to a solid (gel). By adding heat or removing heat these two forms can
be formed. This process can be carried out continually.
Activity pages.
A.
1–E
2–D
3–A
4–C
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5–F
6–B
B.
B1. Student 1 – Raw pineapple has the enzyme Bromelin that breaks down the gel
formation.
B2. Student 2 – More gelatine is used compared to the amount of water and sugar
used in the recipes.
B3. Student 3 – Custard adds to the setting strength of the dessert as it has only
10ml of gelatine is used.
B4. Student 1 or Student 3 – Both those desserts will taste sweet, student’s 3
dessert will have the flavour of the custard and student’s 1 dessert will have the
flavour of the pineapple.
Processing: A Great Gelatine Dessert
Unit 1
1.1. Problem Statement.
There is no box jelly in the cupboard which he knows how to make, and he is
unable to reach the shops to get any as he lives on a farm. He has found a box of
gelatine and a tin of crushed pineapple one of his mother’s favourite fruits, but he
does not quite know how make a dessert with these products. He also cannot
borrow from a neighbour.
Design Brief
Any answer that the students suggest that will show how the students intent to
solve the problem at hand, which should include the pineapple and the gelatine.
Other foods from the farm could be included as well as foods to add flavour, colour
and taste. Decoration could also be considered.
Unit 2
2.1. Proposal and Investigation.
The students need to state in words what they think they are going to make, in
greater detail which includes the pineapple and the gelatine once more and a more
focused view. No recipe should be written out yet.
Specifications of the dessert need to be done, requirements, appropriate to the brief.
These would include equipment, ingredients, and size of the dessert.
A time plan that is comprehensive and convincing.
One may stress the due date here.
Unit 3.
3.1. Initial Ideas and Research.
Three creative ideas neatly drawn with annotated labels and descriptions and all
advantages and disadvantages stated.
Motivation of the most suitable idea written down and a thorough list of challenging
aspects of their idea stated.
Unit 4
Development and Planning.
4.1. Final Idea.
The recipe ingredients should have precise quantities, the method written in the
Standard recipe form being accurate and clear, and the final drawing should be neat,
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labelled coloured and show all views needed to show accurately what the dessert
looks like.
4.2 Planning.
A flow chart drawn which is comprehensive and coherent.
Unit 5.
Making and Evaluation.
5.1 Making.
The student needed to show good tool manipulation and cooking skills. Safety
procedures and cleaning up skills also need to be demonstrated.
5.2. Evaluation.
There are two types of evaluation:
The students need to evaluate their own work by discussing as a group how
successful their dessert is in relation to the marking rubric given to them to follow.
This evaluation should highlight the particular strengths and weaknesses and clarify
any improvements that need to be made to the product. This stage must be
completed before the handing in of the dessert.
Secondly the teacher evaluates the final product using the rubric provided in the
learners’ manual.
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